Currently, the only polling method, is load_balanced.  Doing a simultaneous method would introduce a race condition where all three are notified and could result in strange things happening more often.  Currently this is an existing issue in 2.0, as two people can answer the same chat, which leads to corruption of the chat.  To add a simultaneous method would mean adding a lot of code in various places, so it has been pushed back to the 3.0.0 release (which will have plugable polling methods BTW)